A massive study of US clergy has shown that six in 10 priests and pastors have "never doubted" their call by God, and never considered leaving the profession.

"There's a lot of frustration about working in ministry but overall it is a very rewarding profession," said Rev Jackson Carroll, director of the Pulpit and Pew research project at Duke Divinity School.

The optimistic data from the "Pulpit and Pew" research project at Duke Divinity School is good news to church leaders who are struggling to recruit talented young people as priests and pastors.

"We were surprised that so many clergy were satisfied with their career choice, and so few doubted their call," said the Rev. Jackson Carroll, director of the project.

The four-year project on pastoral leadership involves 20 areas of study, 30 researchers and a $A7 million budget. It covers Protestant, Catholic and other clergy and will look at such topics as salaries, recruitment, firings, media portrayal and leadership.

The findings come from in-depth interviews with 900 clergy and 2500 other responses to mailed questionnaires.